Known discharge units for water treatment generate an electric discharge in water to purify the water. For example, Patent Document 1 discloses this type of discharge unit. The discharge unit of Patent Document 1 includes a pair of electrodes and an insulating divider. The pair of electrodes are provided in water and receives a predetermined voltage from a DC power source. The insulating divider separates the pair of electrodes from each other in the water, and has a through-hole defining a path of current to flow between the pair of electrodes. In this discharge unit, when a DC voltage is applied from the DC power source to the pair of electrodes, the density of current increases along the path of current of the through-hole of the divider to generate an electric discharge. The discharge produces bactericidal factors such as hydroxyl radicals in the water, thereby purifying the water.